Gas turbine engines to which the present invention applies typically have a multiplicity of blades or buckets mounted in adjacent positions extending radially about the periphery of a rotor wheel or disc. Each blade is formed with integral airfoil, platform and root sections, and is mounted platform edge-to-platform edge across a spacing gap with an adjacent blade.
There exists a need in such arrangements to appropriately cool the blades so as to enable them to withstand exposure to high temperature gases. Cooling of the blades is commonly accomplished in part by the circulation of cooler gas in and around the root portion of the blades. An arrangement to seal the gaps between adjacent blades is commonly provided to keep the hot gases from flowing below the platforms and to prevent the outward flow of cooling gases from upsetting the main gas flow.
There also exists a need to dampen the vibration during engine operation between the rotor disc and blades, and between the blades themselves. The occurrence and degree of this vibration is a function of many factors including gas temperature, turbine speed and the method by which the blades are retained within the rotor. Unchecked vibration may lead to blade fatigue failure and cause complications to retaining the blades within the disc.
Prior art blade platform gap sealing and vibration damping arrangements are known that utilize an elongated insert fitted into a complementary shaped slot or pocket formed between the platform edges of adjacent blade structures, so that centrifugal forces acting on the element upon rotation of the rotor drive the insert radially outward to contact the opposing platform edges and seal the gap.
Assembly of such prior art gap sealing systems is, however, time-consuming and costly, typically requiring the careful orientation and positioning of each small insert element into its respective corresponding slot. If an element is inserted with the wrong orientation, proper sealing and damping is precluded. Also, the tolerance needed to ensure proper orientation between the insert and the slot may be so close that centrifugal forces wedge the insert too tightly in the slot, totally blocking cooling of the platform edges. Moreover, on some blade designs there is insufficient room to accommodate such an insert sealing and damper arrangement because of the close proximity of the airfoil to the platform edge in the region of maximum airfoil thickness.